Many integrated circuit devices require bypass or decoupling capacitors connected between the ground and power leads of the integrated circuit device to filter the output of the power supply which supplies power to the device.
In plastic packaged integrated circuits, a lead frame is provided having a plurality of leads that extend from the package. The leads are soldered to bonding pads on a printed circuit board in surface mount technology or to plated through holes in the printed circuit board in through-the-board technology. At least one of the leads is electrically connected via a bonding pad or through hole to a trace on the printed circuit board that supplies ground to the integrated circuit. At least one of the remaining leads is electrically connected via a bonding pad or through hole to a trace on the printed circuit board that supplies power to the integrated circuit.
Typically, the bypass capacitor for a plastic packaged integrated circuit device has a pair of terminals soldered to bond pads or through holes on the printed circuit board. One terminal is electrically connected via a bond pad or through hole and a printed circuit trace to the trace supplying ground to the integrated circuit device. The other terminal is electrically connected via a bond pad or through hole and a printed circuit trace to the trace supplying power to the integrated circuit device. For maximum effectiveness, it is desirable that the bypass capacitor be mounted as close as possible to the packaged integrated circuit device.
Several problems have been discovered that are associated with the mounting of bypass capacitors on printed circuit boards. These include the fact that printed circuit board layout considerations often prohibit the bypass capacitor from being mounted close to the integrated circuit device. This is especially true in situations where a plurality of integrated circuit devices, each having an associated bypass capacitor, must be densely mounted on a printed circuit board. In addition, the fact that the bypass capacitor is mounted directly on the printed circuit board reduces the amount of board space available for other devices or printed circuit traces. Further, where the bypass capacitor is to be mounted on the printed circuit board, there is no convenient way to test the integrated circuit device and the capacitor at the same time in their actual physical relationship prior to assembling components on the circuit board. This inability to test the integrated circuit device and the bypass capacitor together prior to assembling the components on the circuit board reduces integrated circuit yields because of guard band considerations.
A previous attempt to solve these problems is to mount the bypass capacitor inside the plastic package. A consequence of this solution is that the entire device must be discarded when the bypass capacitor goes bad. This is economically undesirable since the integrated circuit die encapsulated in the plastic package is generally much more expensive than the bypass capacitor.